I have been reading some very helpful tips on this site and would like to thank everyone for their insight and experience!!!

I have recently acquired a 2001 Bonneville SLE with 100K miles. After I purchased this vehicle and drove over 40 miles the transmission began to hard shift. Of course I did not diagnose this is a common issue during a test drive.

Bottom line, I just invested money in this car and would like to find a short term fix to avoid spending the $600-$1800 in fixing this issue without destroying what is left of the transmission.

I have noticed a couple of threads suggesting the use of Sea Foam products to help break loose any particulates that may be clogging the PCS and doing a fluid drain. Please let me know your experience with this method as it poses possibly the best short term alternative to replacing the PCS.

Thanks in advance!!

First thing is check the marshmallow mount behind the radiator that holds the tranny in. Have someone put the car in drive (with e brake applied) and gently give the car some gas. If the motor looks like it wants to roll over on it'* back you have a bad mount. They are around $100, but some have used hockey pucks to fix it if you search for the threads.

Also, when mine went bad I noticed it shifted hard when slowly accelerating, but when you accelerate hard the torque from the motor doesn't let the mount relax and it shifts good.

Thanks for the advice. I will check into this as a possible cause for the hard shift.

One thing I forgot to mention, the hard shift only occurs when the transmission is up to tempurature or I have driven the car recently. It also makes a winning noise after about 60 miles of continuous driving that increases in volume from 1st to 2nd to 3rd. Of course, no issues or noise once in drive.

When was the last filter change done on it (if you know).Also check the fluid level and condition. It should be a bright red and should NOT smell burnt. Other than that you could run some chemical through it or have it flushed, but that usually only delays the final failure.

It is very likely this is a common problem with the Pressure Control Solenoid in the transmission. First thing to do is change the filter and fluid, but when you replace the fluid, add a can of Sea Foam Trans Tune.

If it is the PCS, it gets sticky when it gets dirty from normal residue from clutch wear. It is VERY likely there is nothing to worry about in the rest of the transmission.

When I had the problem, the fluid change with Trans Tune only lasted a month. I then added a shift kit for $90 plus fluid and the problem has been solved.

Search "shift kit" and get more info.

After driving the car again this morning, the symptoms are VERY repeatable. I knew just about when it would start acting up and presto.....

I checked the fluid, it does not smell burnt and while it still has a red tone I would not call it "bright" red. Sounds like a fluid change is in order. The guy I bought the car off said it was ready for its 100K service which would indicate the trans fluid. I am assuming this means it has never been changed. Hopefully this will delay the enevitable long enought to come up with the $600-$800. What stock transmission fluid does GM use?

Hawk.....I read that the Sea Foam is supposed to be used right before the change. Are you recomending using it after as well?

Also, maybe I don't understand but what benifit does the shift kit bring to the PCS issue? I would imagine it will make the tranny shift like a pro compared to stock but the issue with the PCS is that it allows max line pressure when max is not needed. The shift kit only changes the caracteristics of the shift, not the line pressure that is applied to the shift. Just trying to understand.

Most likely it hasn't been changed.

There is probably nothing wrong with the transmission except some residue in the fluid that causes the solenoid to stick. There is no need to spend more than $100-$110 for a shift kit and fluid if this is the case.

Dextron III or VI


I don't remember what the instructions say, but what I did is change the fluid and add Trans Tune together. You do not want to overfill the trans so since I needed to make room for the Trans Tune, I just changed the fluid. Your transmission can never be TOO CLEAN. Besides, if the problem is fine residue, why not get rid of as much of it as possible.

If you rode in my car, you would have no idea it had a shift kit. GM has such a sssooooffffffttttt shift, it is fairly ridiculous (not to mention that it reduces the life of the clutches to slip that much). The car now shifts like it should have from the factory. It is still a softer shift than an Acura I drove. It actually made the whole driving experience feel more solid.

The reason the trans is shifting hard is the PCS sticks and takes too long to shift. When the computer sees this, it takes measures to protect the clutches. Since the clutches wear when the are slipping, the computer makes sure they don't slip much, hence the hard shift.

The shift kit changes the springs in the accumulator in a way that has it take the burden off the PCS. Therefore the computer never sees a long shift (because the accumulator didn't allow it) and never causes a hard shift.

Be sure to utilize the "Search" feature. I have written this on many occasions in different posts. You will find a wealth of information with this feature, so don't be bashful.

Thanks for helping me understand Hawk! I did a search for your past comments and found alot of usefull information contained within these threads.

I guess I will be buying some Sea Foam and Tranny fluid for a fun weekend. We will see how she reacts and take it from there.

Just out of curiosity, you posted on 6/25/07 that you just installed this Shifter Kit. How many miles since then and has the issue ever shown back up? Do you frequently drive for more than 40 minutes at one time? Thanks again!!

Haw-

where is the accumulator and shift kit installed on the transmission?

Side cover

pan on the bottom or somewhere else?

Thanks

Mike

BTW I am experencing the same problem.

I first noticed the problem on a drive from Santa Rosa to San Francisco (1 hr) and driving the hills in SF was quite irritating :? Since then I have made dozens of trips to SF with zero symptoms, four or five trips from Santa Rosa to Seattle and have at least 10,000 miles since the shift kit. The trans is working great!